RESUMEN
With the development of nuclear power, efficiently treating nuclear wastes generated during operation has attracted extensive attention. Hydrogels are common adsorbent materials in the treatment of wastewater due to their high swelling rate and easy post-treatment. In this work, a novel polyacrylic acid/crown-ether/graphene oxide (PAA/DB18C6/GO) hydrogel composite was synthesized by a radical cross-linking copolymerization method and characterized using various analytical tools such as SEM, FT-IR, TGA and XPS. The effects of time, pH, initial Sr2+ concentration, and temperature on Sr2+ adsorption onto the PAA/DB18C6/GO were studied. The PAA/DB18C6/GO shows a high adsorption capacity of 379.35 mg g-1 at an initial Sr2+ concentration of 772 mg L-1 due to the unique structure of dibenzo-18-crown-ether-6 and high swelling. The composite has a high selectivity for Sr2+ with a removal rate of 82.4% when concentrations of Na+ and K+ were 10 times higher than that of Sr2+. The pH and temperature have no apparent impact on adsorption performance of the PAA/DB18C6/GO under the experimental conditions. The composite shows excellent reusability with more than 92% removal rate for Sr2+ after five continuous cycles. In addition, the mechanism of Sr2+ adsorption by PAA/DB18C6/GO was analyzed by fitting the adsorption data to the theoretical models and XPS data.
RESUMEN
Rare earth luminescent materials demonstrate significant advantages in lighting and energy saving, and detection etc. In this paper, a series of Ca2Ga2(Ge1-xSix)O7:y%Eu2+ phosphors were synthesized by high-temperature solid-state reaction and characterized by X-ray diffraction and luminescence spectroscopy methods. The powder X-ray diffraction patterns reveal that all the phosphors are isostructural with a space group of P4¯21m. The excitation spectra of Ca2Ga2(Ge1-xSix)O7:1%Eu2+ phosphors exhibit significant overlapping of the host and the Eu2+ absorption bands, which facilitates Eu2+ absorbing the energy to increase its luminescence efficiency when excited by visible photons. The emission spectra show that the Eu2+ doped phosphors have a broad emission band with a peak centered at 510 nm arising from the 4f65d1â4f7 transition. Variable temperature fluorescence reveals that the phosphor has a strong luminescence at low temperature but has a severe thermal quenching effect when temperature rises. The optimal Ca2Ga2(Ge0.5Si0.5)O7:1.0%Eu2+ phosphor shows promise for application in the field of fingerprint identification based on the experimental results.
RESUMEN
Effective removal of strontium isotopes in radioactive waste streams has important implications for the environment and the sustainable development of nuclear energy. In this work, a zirconium phosphate/18-crown-ether-6 (ZrP/18C6) composite was prepared using the intercalation method by loading crown ether into zirconium phosphate. The composite was structurally and morphologically characterized by XRD, FT-IR, XPS, and SEM. The adsorption experiments of Sr2+ onto the ZrP/18C6 composite were conducted as a function of temperature, pH, Sr2+ concentration and competing ions. The results indicate ZrP/18C6 can adsorb 98.6% of Sr2+ within 30 minutes at an Sr2+ concentration of 100 mg L-1 and maintain a high removal rate with a distribution coefficient of 7 × 105 mL g-1 when Sr2+ is at a low level of 4.28 mg L-1. The ZrP/18C6 composite reached a maximum adsorption capacity of 195.74 mg g-1 at an Sr2+ concentration of 380 mg L-1, which is significantly higher than the 43.03 mg g-1 of α-ZrP. The adsorption performance of Sr2+ onto ZrP/18C6 is not significantly affected by temperature, pH and competing ions. Furthermore, the adsorption kinetics and thermodynamics were analyzed based on the adsorption data obtained in the present work. It is shown that the adsorption of Sr2+ onto ZrP/18C6 follows the pseudo-second-order model and the Langmuir monolayer model, respectively. Additionally, the adsorption mechanism of Sr2+ by ZrP/18C6 is discussed.
RESUMEN
Four new double perovskites, SrLaMReO(6) (M = Mg, Mn, Co, Ni) in which Re(5+) (5d(2)) is present, were prepared via conventional solid state reactions and characterized by X-ray and neutron powder diffraction, XANES, SQUID magnetometry, and muon spin relaxation (µSR). Synchrotron X-ray and neutron diffraction experiments confirmed that all compounds crystallize in the monoclinic P2(1)/n structure type, which consists of alternately corner-shared octahedra of MO(6) and ReO(6). Rietveld refinement results indicated anti-site mixing of less than 7% on the M/Re sites. Bond valence sum calculations (BVS) suggest all M and Re ions are 2+ and 5+, respectively, and for the Mn-containing phase this is also supported by XANES measurements. All of the materials are paramagnetic at room-temperature and their Curie-Weiss temperatures are positive (except for Mg) indicating net ferromagnetic interactions. No evidence for long-range magnetic order is evident in the dc magnetic susceptibility and µSR measurements for SrLaMgReO(6) to 2 K. The Mn-phase shows long-range order at T(C) = 190 K and neutron diffraction revealed a ferromagnetic structure with a refined net moment of â¼3.7µ(B). Both Co- and Ni-containing phases exhibit spin glass behavior at T(G) = 23 and 30 K, respectively, which is supported by neutron diffraction and a.c. susceptibility data. The structure and physical properties of these four new rhenium based ordered double perovskites are compared to the closely related "pillared perovskites", La(5)Re(3)MO(16), the isoelectronic Os(6+) (5d(2)) double perovskite Sr(2)CoOsO(6), and the Re(6+) (5d(1)) double perovskites, Sr(2)MReO(6), (M = Mg, Ca, Mn, Co, Ni).
RESUMEN
Synchrotron powder diffraction data from methylammonium tin bromide, CH(3)NH(3)SnBr(3), taken as a function of temperature, reveal the existence of a phase between 230 and 188 K crystallizing in Pmc2(1), a = 5.8941 (2), b = 8.3862 (2), c = 8.2406 (2) A. Strong ferroelectric distortions of the octahedra, associated with stereochemical activity of the Sn 5s(2) lone pair, are evident. A group analysis and decomposition of the distortion modes of the inorganic framework with respect to the cubic parent is given. The primary order parameters driving this upper transition appear to be an in-phase tilt (rotation) of the octahedra coupled to a ferroelectric mode. The precise nature of the lower-temperature phase remains uncertain, although it appears likely to be triclinic. Density-functional theory calculations on such a triclinic cell suggest that directional bonding of the amine group to the halide cage is coupled to the stereochemical activity of the Sn lone pair via the Br atoms, i.e. that the bonding from the organic component may have a strong effect on the inorganic sublattice (principally via switching the direction of the lone pair with little to no energy cost).
RESUMEN
The title compound forms on fusion and annealing of a stoichiometric mixture of the elements. The structure was determined by single-crystal X-ray diffraction methods in the monoclinic space group C2/c, with a = 15.154(3) A, b = 10.401(2) A, c = 17.413(4) A, and beta = 113.57(3) degrees, Z = 8. Four-membered Tl-Sb1-Sb4-Sb3 rings interlinked by pairs of Sb2 bridges generate swinglike repeat units [Tl(2)Sb(8)] that are further interlinked through external Tl-Tl bonds to form infinite one-dimensional chains. Cations play a major role in the structure. In contrast to the Zintl-phase K(6)Tl(2)Sb(3) with similar swinglike [Tl(4)Sb(6)] repeating units and Tl-Tl interlinkages, Na(6)TlSb(4) has a more compact conformation of the chains and a notably smaller cell volume than expected. The new phase is metallic with two excess cations according to empirical electron counting, EHTB band calculations for the anion, and the compound's measured resistivities and magnetic susceptibilities. The notably shorter Tl-Tl bond in the present salt (2.954 A) can be directly attributed to the smaller cation and reduced intercation repulsions across that bond.